Machining tool, especially a milling tool

ABSTRACT

The invention relates to a machining tool, especially a milling tool, comprising a shaft-like holder defining a longitudinal axis ( 13 ), a seat ( 9 ) being provided in the front face of the holder for a cutting plate that can be inserted into said holder. The cutting plate has a coupling part serving for mounting in the seat ( 9 ) of the holder. The coupling part has three ribs which project axially from the end surface of the cutting plate that is opposite the holder and which extend radially. Said ribs are provided for engagement in complementary grooves ( 31 ) configured in the seat ( 9 ) of the holder, the side walls ( 37  and  35 ) thereof forming driving surfaces and support surfaces, which interact for transmitting a machining torque, or as axial position safety-catch, with corresponding surfaces of the flanks of the ribs of the cutting plate. The driving surfaces and the supporting surfaces are formed by limited partial surfaces ( 43  and  41 ) of the side walls ( 37  and  35 ) of the grooves ( 31 ) whose other surfaces are retracted in relation to said partial surfaces ( 43  and  41 ) with the purpose of forming a spacing between the ribs and the walls of the grooves ( 31 ).

The invention relates to a machining tool, especially a milling tool, having a shaft-like holder defining a longitudinal axis on the frontal surface of which there is provided a seat for a cutting plate which may be mounted on the holder, this cutting plate having at least one cutting edge projecting radially from a central body having a bore coaxial with the longitudinal axis for a fastening screw securing the cutting plate axially on the seat of the holder and having a coupling component for mounting on the seat of the holder having three ribs projecting axially from the end face of the body facing the holder and extending radially, which ribs are provided for engagement in complementarily configured grooves on the seat of the holder, the side walls of the grooves forming driving surfaces and support surfaces which operate in conjunction with coordinated surfaces of the flanks of the ribs for transfer of operating torque or for securing the axial position.

Machine tools of this type have been disclosed. DE 34 48 086 C2 discloses a tool of this kind which has a cutting edge and is provided for inside machining of a rotating workpiece. The cutting force active on the cutting plate generates an operating torque relative to the shaft-like holder which is to be transferred between holder and cutting plate by way of the driving surfaces. In the case of a rotating machine tool such as a milling tool, in which the shaft-like holder is connected to a drive spindle, the operating torque generating the cutting force is transferred from the shaft-like holder to the cutting plate by way of the driving surfaces.

Machine tools of this kind are often used for machining processes to be performed with high precision. Reliable and precisely defined positioning of the cutting plate on the seat of the holder is of decisive importance in ensuring adherence to the narrow tolerances required and production of machined surfaces of high quality. In this respect particular attention must be devoted in production to achievement of the greatest possible precision of the geometry of the areas of the cutting plate adjoining the driving surfaces and support surfaces. Because of the properties of the material of the cutting plates this results in high production costs, since the sintered blanks forming the hard metal cutting plates are difficult to machine.

The object of the invention is to produce a machine tool which meets the high requirements to be set but is characterized by comparatively low production costs.

It is claimed for the invention that this object is attained in the case of a machine tool such as that indicated in the foregoing in that the driving surfaces and the support surfaces are made up of limited component surfaces of the side walls of the grooves the other surfaces of which are retracted from these component surfaces to form a space between the ribs and the walls of the grooves.

In that, as claimed for the invention, the bearing areas on which the cutting plate is fixed in position on the seat and secured by the fastening screw are only in the form of the component surfaces on the side walls of the grooves, production is simplified, since, in contrast to the contact over the entire area between the ribs of the cutting plate and the grooves of the seat of the holder, correspondingly narrow tolerances need be specified only for the bearing surface areas. In other words, the accuracy of positioning of the cutting plate on the seat is not disturbed by any surface errors present outside the limited bearing areas should such errors occur on the retracted areas present outside the bearing areas.

The dimensions determined for the component surfaces of the grooves of the seat forming the driving surfaces and the support surfaces preferably are such that contact on the flanks of the ribs of the cutting plate occurs more or less only as linear contact, preferably on the areas of the ribs positioned radially on the exterior, and accordingly at a correspondingly great radial distance from the longitudinal axis of the tool, so that appropriate axial spacing is created for transfer of the operating torque generated by the action of the cutting force.

All the component surfaces making up the bearing areas may be in the form of wall components projecting as ribs in alignment opposite each other which are provided on both side walls of the seat of the holder. These wall components projecting as ribs preferably are positioned on the radially exterior end area of the grooves. As an alternative or in addition, the configuration may be such that the path of the side walls of the grooves diverges slightly from the outer end to the inner end adjacent to the longitudinal axis, so that the clearance between the side walls in the radially inner area is larger than in the outer area of the grooves and is larger than the corresponding width of the ribs of the cutting plate. In a configuration such as this the outer end areas of the grooves, which are positioned at a smaller distance from each other, always form the component surfaces serving as bearing areas in relation to which the areas of the walls positioned farther inward radially are positioned farther away because of the slightly divergent path of the side flanks of the ribs of the cutting plate.

In especially preferred exemplary embodiments wall components projecting as ribs are provided on the outer end area of the grooves as bearing component surfaces, along with a path of the side walls in the grooves diverging slightly radially inward from the bearing area.

By preference the geometry and the dimensioning selected for the flanks of the ribs of the cutting plate and of the component surfaces of the grooves of the seat of the holder forming the bearing areas are such that, when the cutting plate is in contact with the seat of the holder, an intervening space is provided between the end surface of the cutting plate and the facing frontal surface of the seat of the holder, so that any surface defects present on the areas of the cutting plate situated outside the bearing areas of the cutting plate and the seat of the holder are insignificant.

In order to reduce the danger that fouling of the intervening space might be caused by penetration of machining residue during operation, an edge area projecting slightly from the frontal surface of the circumference of the seat of the holder may form a circumferential local reduction of the intervening space between end surface of the cutting plate and facing frontal surface of the seat of the holder.

Reference will now be made in detail to the exemplary embodiment of the invention in which

FIG. 1 presents a side view of an exemplary embodiment of the machine tool claimed for the invention in the form of a milling tool;

FIG. 2 a perspective detached view on a scale larger than that of FIG. 1 of the frontal end area of the exemplary embodiment with the cutting plate raised from the seat of the holder, the central fastening screw securing the cutting plate axially on the seat being omitted;

FIG. 3 a perspective view similar to that of FIG. 2, but in the line of sight to the end surface of the cutting plate facing the seat of the holder;

FIG. 4 a top view more greatly enlarged in comparison to that of FIGS. 2 and 3, exclusively of the seat of the holder of the exemplary embodiment; and

FIG. 5 a greatly enlarged representation of the section designated as V in FIG. 1.

The invention will be explained with reference to an exemplary embodiment which is that of a machine tool in the form of a milling tool the cutting plate 1 of which has four cutting edges 3 which project radially from a central body 5 circular in outline. The body 5 has a central bore 7 for a fastening screw (not shown) by means of which the cutting plate 1 may be secured on a seat 9 which is configured on the frontal end of a holder 11 in the form of a milling shaft having a longitudinal axis 13. The seat 9 has a threaded bore 15 coaxial with the longitudinal axis 13 for the fastening screw (not shown) for securing the cutting plate 1. This fastening screw has a cone-shaped section which, in conjunction with a tapered surface 17 which is situated in the vicinity of the exterior end area of the bore 7 and extends this bore 7 outward, contributes to centering of the cutting plate 1 on the seat 9 of the holder 11.

Rather than the exemplary embodiment presented, in the form of a rotating milling tool, the invention might also assume the form of a non-rotating machine tool used, for example, for inside machining of a rotating workpiece, a tool in which the cutting plate might be provided, for example, with only one cutting edge. In both instances operating torque acting around the longitudinal axis 13 by interaction of seat 9 of the holder 11 and cutting plate 1 is to be transferred.

For the purpose of axial positioning and transfer of torque the cutting plate 1 has on its end surface 19 facing the holder 11 (FIG. 3) a coupling component with three axially projecting ribs 21 which enclose the same central angles relative to each other and which extend in the radial direction from the central bore 7 to the circumference of the end surface 19 on the body 5 of the cutting plate 1. As shown particularly in FIG. 3, the ribs 21 have tapering side flanks 25 and 27 (see FIGS. 3 and 5), the angles of inclination of these flanks 25 and 27 varying and the inclination of the flank 27 being steeper than that of the flank 25.

The seat 9 of the holder 11 has formed in its frontal surface 29, which is situated in a normal radial plane perpendicular to the axis 13, three grooves 31 complementary to the ribs 21 in the frontal surface 29, the side walls of these grooves being designated as 35 and 37. The inclination of the side walls 35 and 37 corresponds to the inclination of the flanks 25 and 27 of the ribs 21 of the cutting plate 1. The plane groove base of the grooves 31 is designated as 39, see FIGS. 2 and 5.

As shown in FIG. 4, the grooves 31 are very slightly wider in their interior end area than on their exterior end extending radially relative to the axis 13. In the area of this exterior end there is on each side wall 35 and 37 a wall component 41 and 43 projecting slightly in the form of a rib, these wall components 41 and 43 being aligned with each other and forming an additional slight local narrowing of the grooves 31. These component surfaces made up of wall components 41 and 43 from which the other surfaces of the side walls 35 and 37 are retracted represent the only support surfaces of the seat 9 with which parts of the ribs 21 of the cutting plate 1 come into contact. As shown particularly in FIG. 5, which illustrates the radially exterior end of a groove 31 and the corresponding outer end of a rib 21 introduced into this groove, the side flank 27 of the rib 21 is in contact with the projecting wall component 43 and the flank 25 of the rib 21 is in contact with the projecting wall component 42 of the groove 31. There is a space between the groove base 39 and the top surface 23 of the rib 21.

The side flank 27 is represented by the more steeply inclined flank of the rib 21. The surface of the wall component 43 adjoining the flank 27 forms a driving surface for transfer of the operating torque caused by the cutting force (see arrow 45). The opposite projecting wall component 41 of the groove 31 forms the component surface belonging to the bearing area and serving as additional support surface.

The remaining side wall components of the grooves 31 are retracted even farther from the flanks 25 and 27 of the ribs 21 by the inwardly radial divergent path of the side walls 35 and 37 of the grooves 31.

As shown the most clearly in FIG. 5, there is between the end surface 19 on the body 5 and the frontal surface 29 on the seat 9 an intervening space 47 when the side flanks 25 and 27 are in contact with the bearing area of the grooves 31. An edge 49 which projects slightly in the axial direction and encloses the frontal surface 29 of the seat on the circumference, effects local reduction of the intervening space as protection from penetration by fouling matter.

The bearing component surfaces of the grooves 31 formed by the projecting wall components 41 and 43 by which the wall components 43 form driving surfaces and the wall components 41 form support surfaces for the ribs 21 could be replaced by different configurations of the side walls 35 and 37 of the grooves 31 which form limited component surfaces functioning exclusively as bearing areas. Hence, the formation of limited component surfaces defining the bearing areas of the component surface could be effected exclusively by the divergent configuration of the side walls of the grooves, that is, without projecting wall components 41 and 43. 

1. A machining tool, especially a milling tool, having a cutting plate (1) and a shaft-like holder (11) defining a longitudinal axis (11) on the frontal surface of which there is provided a seat (9) for a cutting plate (1) which may be mounted on the holder (11), this cutting plate (1) having at least one cutting edge (3) projecting radially from a central body (5) having a bore (7) coaxial with the longitudinal axis (13) for a fastening screw securing the cutting plate (1) axially on the seat (9) of the holder (11) and having a coupling component for mounting on the seat (9) of the holder (11) having three ribs (21) projecting from the end face of the body and extending radially, which ribs (21) are provided for engagement in complementarily configured grooves (31) on the seat (9) of the holder (11), the side walls (35, 37) of the grooves (31) forming driving surfaces and support surfaces which operate in conjunction with coordinated surfaces of the flanks (27 and/or 25) of the ribs (21) for transfer of operating torque or for securing the axial position, characterized in that the driving surfaces and the support surfaces are formed by limited component surfaces (43 and 41) of the side walls (37 and/or 35) of the grooves (31) the other surfaces of which are retracted from these component surfaces (43 and 41) for the purpose of forming a space between the ribs (21) and the walls of the grooves (31), and in that all component surfaces are in the form of rib-like projecting wall components (41, 43) which wall components (41, 43), in alignment opposite each other, are provided on both side walls (35, 37) of the grooves (31) of the seat (9) of the holder (11).
 2. The machine tool as claimed in claim 1, wherein the component surfaces (43, 41) of the grooves (31) on the seat (9) of the holder (11) forming the driving surfaces and the support surfaces are provided for the more or less linear contact on the radially exterior end areas of the ribs (21) of the cutting plate (1) at an appropriate radial distance from the longitudinal axis (13).
 3. The machine tool as claimed in claim 1, wherein the side walls (35, 37) of the grooves (31) extend on a slightly divergent path from the exterior end toward the interior end adjacent to the longitudinal axis (13), so that the clearance between the side walls (35, 37) in the radially interior area is greater than in the exterior area of the grooves (31) and greater than the corresponding width of the ribs (21) of the cutting plate (1).
 4. The machine tool as claimed in claims 1, characterized by an intervening space (47) between the end surface (19) of the cutting plate (1) and the facing frontal surface (29) of the seat (9) of the holder (11) when the flanks (25, 27) of the ribs of the cutting plate (1) are in contact with the associated component surfaces (41, 43) of the grooves (31) of the holder (11).
 5. The machine tool as claimed in claim 4, characterized by an edge (49) on the circumference of the seat (9) projecting a short distance axially from the frontal surface (29) of the seat (9) of the holder (11), which edge (49) forms a circumferential local reduction of the intervening space (47) between the end surface (19) of the cutting plate (1) and the facing frontal surface (29) of the seat (9) of the holder (11).
 6. The machine tool as claimed in claims 1, wherein the flanks (25, 27) of the ribs (21) of the cutting plate (1) and the side walls (35, 37) of the grooves (31) of the holder (11) follow a path inclined at an angle varying in value relative to the plane perpendicular to the longitudinal axis (13) and wherein the angle of pitch is steeper on the side forming the driving surface for transfer of operating torque than it is on the side forming the support surface. 